Systems are known in the art for the optical analysis of a stream of grain. As the grain is harvested in the field, a light source passes light through the grain stream. The transmitted light is detected by a receiver and processed by a computer under software control. By comparing the spectral absorption with values representing known absorption, the grain can be analyzed to determine its constituents. Examples of systems for handling grain are disclosed in U.S. Pat. Nos. 5,343,761 and 5,369,603, both of which are incorporated herein by reference.
To make that determination, a reference value is used. For example, the light can be transmitted to a white ceramic tile without grain present. The light reflected and received from the tile provides a reference value for use in analyzing the light as reflected from the grain. The use of a tile can have disadvantages. It can become dusty, particularly from the grain, and the dust can affect the light reflected from the tile. Therefore, the dust can alter the reference value and affect the accuracy of the analysis. In addition, the use of a tile to obtain a reference value only works for analyzing a signal reflected from the grain, since the reference is obtained from a reflected signal. Other references must be used for analyzing a signal transmitted through the grain.
Accordingly, a need exists for improvements in these systems for optical analysis of agricultural products.